Klausmobile Tube Tester Files

09/1991, maker unknown. Of the few tubes of this type this one is the best, not microphonic and the triode specs are unbelievable! 20 mA/V and Mu of 100+ is something you don't find too often! An input tube in a 2-stage phono preamp? This one was unused in factory box, with invisible heater design. Two types of this tube exist: one (right) is traditional, where you can see glowing heater protruding slightly above upper mica. The other (left - apparently better built mechanically) has relatively large screen (sheet steel), wrapping around above upper mica, so neither heater is visible (it's under that wrapped screen). Go for this type only!

1. Triode section

Standard specifications per each triode
Parameter Maximum Operating Point Measured *
Ua, V +300 150V 160
Ug, V - (0.8) -1.0
Ia, mA 22 12.5 10
Pa, W 3 (?) (1.7) 1.6
Gm, mA/V - 19 17
Rp, kOhm - - 6.2
Mu, V/V - - 105

(*) the tube can reach specified DC point precisely, but it's too close to grid current zone, so I stepped down to keep safe.

1.1. Full power curves @ 6.3V heater

1.2. 8mA closeup. One set for 5V heater, another 6.3V heater. Apart from grid level shift (1/4V), no visible changes! Where only one Ug tag per two curves is visible, it is for +6.3V curve.

1.3. And for the pizzazz. Gm/Mu/Rp measurements. Ug operating area is quite narrow, it should be. I am afraid these measurements are not too precise. To calculate differentials, my hardware steps dUg=-0.25V, dUa=-2.5V. This is alright for a typical small tube, but 1/4V Ug stepping is too much for this tube - actual Gm is somewhat higher than in these tables.

2. Pentode section in triode mode

So far I cannot test it fully - my hardware oscillates wildly with this tube. Anyway, DC measurements with batteries show that this tube's pentode in triode wiring is as capable as it's partner. The operating point is around Ua=150V, Ia=10mA, Ug=-1.0V, Gm=12-18 mA/V, Mu=70, Rp=5..4 kOhm. Not bad at all!

Too bad, the other 6F12Ps in a batch (of different design, year and origin) all showed serious (50-200uA) plate-to-control-grid leakage current. Either dirty tubes or just dying, who knows.

Legend: White curves: Ig<5uA Yellow: 5<Ig<20uA Red: 20<Ig<300uA. Measurements terminate at Ig>300uA

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